BAITED UNDERWATER VIDEO
Ever wondered how scientists count fish?
One method that is used widely around New Zealand and the world is Baited Underwater Video (BUV).
This method uses bait to attract fish in front of a camera. Researchers can then count the fish on the video to get an idea of species abundance and diversity.
HOW IT WORKS
HOW IT LOOKS
The BUV we use has a metal frame that holds a camera overlooking a bait pot. On the lower arm of the frame, there are black marks which give the observer an idea of how big the fish are. Each mark is 10cm long.
The top of the frame is tied to two floats. One of the floats is underwater with the frame and helps to keep the frame upright. The other float is on the surface and is to help the boat find the camera again when the trial is over.
HOW IT RUNS
To run a BUV trial, researchers lower the frame over the side of the boat. When the frame touches the seafloor the trial begins. We run our BUV trials for 30 minutes. Once the time is up, you pull the BUV back to the surface and download the video footage for analysis.
When researchers do a BUV survey of an area, they will repeat this process over and over in different locations. The more replications (or trials) you do, the more confident you can be that your results are accurate.
Pākirikiri, Rāwaru Parapercis colias
For our BUV's, we're analysing the number of Blue Cod!
Why Blue Cod you ask? Well, firstly they're endemic to New Zealand and inhibit open reef areas or sand and gravel near patch reefs... it's also one of the most common caught recreational fish in South Taranaki, and our fishing survey's indicated Project Reef as a possible Blue Cod nursery!
3 COLOUR PHASES
Scroll over each image to discover the three colour phases of Blue Cod!
A big thank you to Dr Malcom Francis who's wonderful book 'Coastal Fishes of New Zealand' contains the following images of & information on Blue Cod!
Coastal Fishes of New Zealand has been Project Reef's 'go to' book for identification, biology & behaviour for fish!
TRY IT YOURSELF!
When we watch BUV footage, there is no way of knowing if the fish that swims in during the first minute is different from a similar-looking fish that swims in 5 minutes later. We don’t want to be counting the same fish twice! To avoid this, we take the one frame of the video that has the most fish in it and use that as our count for that trial.
You can try doing this for the video below. Try pausing the video every 30 seconds and counting the number of blue cod. You could even pause it every 10 seconds if you wanted to be more accurate!
Snapper eat virtually any animal matter, and diet changes with size.
One of the largest carnivores on the reef is the octopus!
SEVEN GILL SHARK
These sharks investigate objects by bumping them with their snouts.
These fish have three colour phases... juvenile, female and male.
These sharks are nocturnal, usually sluggish & are not dangerous.